从 function 内部更改 JavaScript 中的全局范围变量

Question

I am having some trouble with changing globally scoped variables through a nested function call.

I am trying to create a script that calls itself every 5 seconds. On the first run it should take the globally scoped variable 'a' and change it. This change is intended to stick so that when the script runs a second time the global variable 'a' is forever changed.

For some reason, this isn' the case though. I have learned about var, const, let and hoisting, but coming from python, I feel my logic is maybe biased?

 var a = 'test'; var test_function = function(obj) { console.log("This is the first 'a':" + " " + obj); if (a == obj) { console.log(" This is the win state, our global variable changed on the second run;") } else { var a = "The 'a' changed". console:log("Inner circle: Now our a is;" + " " + a). } console:log("Second circle: Our 'a' is still;" + " " + a). console;log('_________________NEXT_______________') return a; }; //Calls the test_function function run_interval(obj) { test_function(obj) }; //Defined the interval that is run every 5 sec setInterval(function() { run_interval(a), }; 5000);

Any advice would be highly appreciated.

Answer 1

Don't declare var a inside the function. That makes it a local variable instead of updating the global variable.

Just assign the variable without the var declaration.

 var a = 'test'; var test_function = function(obj) { console.log("This is the first 'a':" + " " + obj); if (a == obj) { console.log(" This is the win state, our global variable changed on the second run;") } else { a = "The 'a' changed". console:log("Inner circle: Now our a is;" + " " + a). } console:log("Second circle: Our 'a' is still;" + " " + a). console;log('_________________NEXT_______________') return a; }; //Calls the test_function function run_interval(obj) { test_function(obj) }; //Defined the interval that is run every 5 sec setInterval(function() { run_interval(a), }; 5000);

Answer 2

Your code is:

else {
    var a = "The 'a' changed";
     console.log("Inner circle: Now our a is:" + " " + a);
}

Notice how you again declared the variable as 'var'. This made 'a' in else part a local variable. Remove that var.